This invention relates generally to a power controller for industrial applications and, more particularly, to a heat sink for a silicon controlled rectifier (SCR) power controller.
Power controllers are used in industrial applications to regulate power supplied to machinery, manufacturing equipment, and support systems such as heating and air conditioning systems, for example. In general, a power controller provides the interface between an electrical utility (e.g., user owned power generating facility or other supplier) and the electrical distribution network being served by the power supplied by the electrical utility. The power controller typically functions to supply power to using equipment under normal operating conditions, as well as to interrupt the supply of power in the event of overloads or other extraordinary circumstances, to prevent damage to the network and the equipment connected to the network.
In many industrial applications, power controllers require large, expensive installations involving numerous switches, sensors, and indicators for automatically distributing power through the electrical distribution network. Furthermore, if there is a possible malfunction with the power controller, it is important to be able to shut down the power controller in a controlled manner to prevent damage to the using equipment.
Most large electrical resistance heaters utilize a three-phase circuit in which each circuit is individually fused. For a particular installation, a power controller may handle three-phase voltages of between 208Vac to 600Vac, with currents ranging from 50A to 2500A. In such applications, a silicon controlled rectifier (SCR) type power controller may be used to regulate the amount of electricity supplied to the resistive load of a heater. For example, the power controller may employ SCRs gated on to allow current flow in a particular direction. Once gated into conduction, each SCR will continue conducting until current flow in the desired direction stops. For alternating current (AC) power distribution networks, each SCR is gated into conduction for each half-cycle of the AC input wave form during which current flows to a particular phase.
The output of a SCR type power controller is often connected to a power distribution unit and to a number of three-phase fuse blocks. For example, the output may be wired to six or eight of such fuse blocks. In addition, the power controller also may include a firing unit or firing package having outputs connected to respective; gate inputs of each SCR. In such cases, control or gate inputs for the SCRs are supplied as inputs to the circuitry within the firing package, which in turn produces output signals for gating the SCRs into conduction at the proper times.
Every component of a power controller consumes valuable panel space and necessitates additional wiring to make electrical connections between components. Because each electrical connection represents a potential problem and increases the cost of a unit by requiring additional labor and materials, minimizing the number of connections is a continuous goal.
To date, power controllers have not been designed so as to minimize connections and reduce initial cost. For example, existing power controllers provide very limited access to components and only few options for running the power wiring. In particular, such power controllers typically include only a single opening in a side of the unit for running wiring in and out of the same end or at most two openings in opposed sides for running wiring in one end and out of the other end. Consequently, it is often necessary to bend power wiring within and/or around the power controller to accommodate various designs. In large power controllers, several square feet of space may be required for bending the power wiring so that proper electrical connections can be made. The space and bending radius of power wiring can easily exceed the footprint of the power controller, resulting in a much larger unit than would otherwise be necessary.
Moreover, in power controllers that are closed or xe2x80x9ctouch safe,xe2x80x9d wiring becomes even more complicated. Power controllers that are xe2x80x9ctouch safexe2x80x9d generally include a door, hinged top, or other cover for shielding components that become hot to the touch during use. Such protective measures further limit access to components and the ways in which the power wiring can be routed.
Accordingly, there exists the need for a compact, versatile, and xe2x80x9ctouch safexe2x80x9d power controller having a cost-effective design that accommodates multiple electrical connections for various power applications.
Furthermore, SCR power controllers are not perfect conductors and exhibit some voltage drop across the SCRs. When current is flowing through the SCRs, the voltage drop generates heat. Heat must be removed from the SCRs so that a safe operating temperature is not exceeded causing failure of the controller. Some manufactures have provided a thermostat mounted on a heat sink to shut down the SCR power controller if temperature approaches the point where the SCR may be damaged. There are two problems with this approach. The first is that thermostats have proved very inaccurate, and the other is that shutting down production with no warning can prove very costly in many industrial processes.
Accordingly, there exists the need for a power controller having an improved mechanical design and self temperature monitoring capabilities.
In one general aspect, a power controller includes a switching device and a heat sink in contact with the switching device for dissipating heat generated by the switching device. The heat sink may include a base and a plurality of fins extending from the base. The power controller may include a fan for forcing cooling air toward the heat sink and an air guide mounted to the heat sink for dividing the cooling air such that cooling air flows over the top of the heat sink and cooling air flows through the fins of the heat sink.
Implementations may include one or more of the following features. For example, the air guide may be adjusted to set a percentage of cooling air that flows over the top of the heat sink fins and a percentage of cooling air that flows through the fins of the heat sink. The air guide may complete a plenum chamber for forcing cooling air through the power controller. The air guide may be constructed of a single piece.
The power controller may include a bus bar mounted to the switching device. The bus bar may be exposed to the cooling air flowing over the top of the heat sink and may provide additional dissipation of heat generated by the switching device. The power controller also may include a fan for housing the fan and forming an end of the power controller. The power controller may include a ventilated back plate for exhausting the cooling air and forming an end of the power controller. The ventilated back plate may have a plurality of exhaust holes on a top surface and/or side surface thereof.
In another general aspect, a power controller includes a first switching device and second switching device, a first heat sink in contact with the first switching device for dissipating heat generated by the first switching device, and a second heat sink in contact with the second switching device for dissipating heat generated by the second switching device. The first heat sink may include a base and a plurality of fins extending from the base, and the second heat sink may include a base and a plurality of fins extending from the base.
Implementations may include one or more of the following features. For example, the base of the first heat sink may be mounted to the base of the second heat sink to form a heat sink assembly. Adjacent sides of the bases of the heat sinks may be pinned together. The first heat sink may be mounted to the second heat sink using a metal bar. A first side plate of the power controller may be mounted to an adjacent side of the base of the first heat sink and a second side of the power controller may be mounted to an adjacent side of the base of the second heat sink. A fan bracket of the power controller may be mounted to an adjacent side of the base of the first heat sink and an adjacent side of the base of the second heat sink. A back plate of the power controller may be mounted to an adjacent side of the base of the first heat sink and an adjacent side of the base of the second heat sink.
In some cases, the power controller may include a third switching device and a third heat sink in contact with the third switching device for dissipating heat generated by the third switching device. The third heat sink may include a base and a plurality of fins extending from the base. The base of the second heat sink may be mounted to the base of the third heat sink to form a heat sink assembly.
In another general aspect, a power controller includes a switching device, a heat sink contact with the switching device for dissipating heat generated by the switching device, a semiconductor temperature sensor mounted to the heat sink, and an alarm for generating a warning signal in response to the semiconductor temperature sensor. The warning signal may occur prior to shut down of the power controller. The heat sink may include a base and a plurality of fins extending from the base.
Implementations may include one or more of the following features. For example, the semiconductor temperature sensor may be potted in a crimp lug. The power controller may include multiple heat sinks. Each heat sink may include a temperature sensor mounted therein. The alarm may be configured to generate a warning signal in response to each temperature sensor.